Many of the advantages that brushless electric machines such as alternators, for example, have over brush type alternators result from the use of a stationary field coil. An electric machine with a stationary field coil does not require sliding electrical contacts such as brushes and commutators. Having a stationary field coil, however, necessitates that pole segments, of pole pieces, rotate in close proximity to the stationary field coil. Typically the pole segments are positioned radially outwardly of the field coil and radially inwardly of a stator with small annular air gaps therebetween. Since a brushless alternator has no sliding contacts, current to the field coil is typically supplied through stationary conductors routed through an axial end of the machine to the field coil; typically this is the same axial end that structurally supports the field coil. In such a design the rotatable poles are fixedly attached to the shaft and the pole segments are cantilevered in the annular space between the field coil and the stator. This cantilevered attachment of the pole segments to the shaft is along an axial end of the shaft that is opposite the end from which the conductors are routed to the field coil.
The cantilevered poles, however, limit the rotational speed at which the alternator can rotate. This rotational speed limitation is partially due to radially outward flexing of the pole segments that results from the high centrifugal forces on the pole segments that occurs at high rotational speeds, which can result in undesirable contact of the flexed pole segments with the stator. Efforts to control such flexing usually add undesirable mass, and consequently, undesirable inertia to the rotational components of the assembly. As such, the industry would be receptive to brushless machines that overcome the foregoing deficiencies.